Encapsulated sodium nitrite as a new toxicant for possum control in New Zealand

Abstract

Sodium nitrite (NaNO 2 ), a commonly used food preservative, has been researched in New Zealand for the control of brushtail possums (Trichosurus vulpecula). In sufficiently high doses, NaNO 2 is toxic because it disrupts circulatory transport of oxygen. As NaNO 2 is very bitter, encapsulation and mixing it through a highly palatable bait formulation is necessary to effectively deliver it to target pest species. In no-choice cage trials, 12/12 possums consumed a lethal dose of toxic paste bait and died on average after 95.6 minutes (±4.9 SE). In two-choice cage trials 7/8 possums consumed a lethal dose of toxic paste bait and died on average after 96.7 minutes (±11.4 SE). Two field trials targeting possums using this toxic paste in bait stations reduced their abundance by 81.2% (± 2.5% SE) and 72.7% (± 1.6% SE) respectively. NaNO 2 paste, known as BaitRite, has been registered in New Zealand as a vertebrate toxic agent for controlling possums.

Secondary poisoning risk for encapsulated sodium nitrite, a new tool for possum control

“…Trials on possums and feral pigs with baits containing encapsulated NaNO 2 have demonstrated high efficacy (>80%) (Shapiro et al 2015(Shapiro et al , 2016. The effects from a lethal dose of bait are comparable to those previously observed on stoats, cats and foxes dosed with PAPP, a toxin that is also considered to be relatively more humane than currently registered toxins used for these species such as 1080 (Marks et al 2004;Beausoleil et al 2010; Eason et al 2010Eason et al , 2014Murphy et al 2011).…”

“…Encapsulated sodium nitrite (NaNO 2 ) in a paste bait was registered in New Zealand in 2013 by the Agricultural Compounds and Veterinary Medicines (ACVM) group for the control of brushtail possums and feral pigs (Sus scrofa). It has provided an effective addition to current control techniques for these two pest species (Shapiro et al 2015(Shapiro et al , 2016. NaNO 2 is commonly used at low concentrations as a colour fixative and preservative in meats and fish (Binkerd & Kolari 1975;Epley et al 1992).…”

“…Levels of MtHb in the blood above 70% are usually fatal, creating a lethal deficit of oxygen in cardiac muscle and the brain, and the resulting rapid lack of oxygen to the brain and other vital organs quickly leads to death from respiratory failure (Wright et al 1999;Eason et al 2010). For mammals the common signs of severe methaemoglobinaemia include shortness of breath, cyanosis, lethargy, loss of consciousness and bluish colouring of the skin especially in areas of high blood supply like lips, gums, hands/paws and nose (Kennedy et al 1997;Wright et al 1999;Eason et al 2014;Shapiro et al 2015Shapiro et al , 2016. In possums, death after a lethal dose usually occurs within 2 hours after bait has been consumed, with clinical signs first appearing within 15 to 35 minutes (Shapiro et al 2016).…”

“…For mammals the common signs of severe methaemoglobinaemia include shortness of breath, cyanosis, lethargy, loss of consciousness and bluish colouring of the skin especially in areas of high blood supply like lips, gums, hands/paws and nose (Kennedy et al 1997;Wright et al 1999;Eason et al 2014;Shapiro et al 2015Shapiro et al , 2016. In possums, death after a lethal dose usually occurs within 2 hours after bait has been consumed, with clinical signs first appearing within 15 to 35 minutes (Shapiro et al 2016). Animals become lethargic and sleepy before they die and, at high doses, NaNO 2 induces a relatively fast time to unconsciousness compared to most currently registered toxins (Shapiro et al 2016).…”

“…In possums, death after a lethal dose usually occurs within 2 hours after bait has been consumed, with clinical signs first appearing within 15 to 35 minutes (Shapiro et al 2016). Animals become lethargic and sleepy before they die and, at high doses, NaNO 2 induces a relatively fast time to unconsciousness compared to most currently registered toxins (Shapiro et al 2016). Encapsulated NaNO 2 also has the benefit of an antidote (methylene blue).…”